//! Renderer for `zterm`.

/// Double-buffered intermediate rendering pipeline
pub const Buffered = struct {
    allocator: Allocator,
    created: bool,
    size: Point,
    screen: []Cell,
    virtual_screen: []Cell,

    pub fn init(allocator: Allocator) @This() {
        return .{
            .allocator = allocator,
            .created = false,
            .size = undefined,
            .screen = undefined,
            .virtual_screen = undefined,
        };
    }

    pub fn deinit(this: *@This()) void {
        if (this.created) {
            this.allocator.free(this.screen);
            this.allocator.free(this.virtual_screen);
        }
    }

    pub fn resize(this: *@This()) !Point {
        const size = terminal.getTerminalSize();
        if (meta.eql(this.size, size)) return this.size;

        this.size = size;
        const n = @as(usize, this.size.x) * @as(usize, this.size.y);

        if (!this.created) {
            this.screen = this.allocator.alloc(Cell, n) catch @panic("render.zig: Out of memory.");

            this.virtual_screen = this.allocator.alloc(Cell, n) catch @panic("render.zig: Out of memory.");
            @memset(this.virtual_screen, .{});

            this.created = true;
        } else {
            this.allocator.free(this.screen);
            this.screen = this.allocator.alloc(Cell, n) catch @panic("render.zig: Out of memory.");

            this.allocator.free(this.virtual_screen);
            this.virtual_screen = this.allocator.alloc(Cell, n) catch @panic("render.zig: Out of memory.");
            @memset(this.virtual_screen, .{});
        }
        try this.clear();
        return size;
    }

    /// Clear the entire screen and reset the screen buffer, to force a re-draw with the next `flush` call.
    pub fn clear(this: *@This()) !void {
        try terminal.clearScreen();
        @memset(this.screen, .{});
    }

    /// Render provided cells at size (anchor and dimension) into the *virtual screen*.
    pub fn render(this: *@This(), comptime Container: type, container: *Container, comptime Model: type, model: *const Model) !void {
        const size: Point = container.size;
        const origin: Point = container.origin;
        const cells: []const Cell = try container.content(model);

        if (cells.len == 0) return;

        var idx: usize = 0;
        var vs = this.virtual_screen;
        const anchor: usize = (@as(usize, origin.y) * @as(usize, this.size.x)) + @as(usize, origin.x);

        blk: for (0..size.y) |row| {
            for (0..size.x) |col| {
                vs[anchor + (row * this.size.x) + col] = cells[idx];
                idx += 1;

                if (cells.len == idx) break :blk;
            }
        }
        // free immediately
        container.allocator.free(cells);

        for (container.elements.items) |*element| try this.render(Container, element, Model, model);
    }

    /// Write *virtual screen* to alternate screen (should be called once and last during each render loop iteration in the main loop).
    pub fn flush(this: *@This()) !void {
        try terminal.hideCursor();
        // TODO measure timings of rendered frames?
        var cursor_position: ?Point = null;
        var writer = terminal.writer();
        const s = this.screen;
        const vs = this.virtual_screen;
        for (0..this.size.y) |row| {
            for (0..this.size.x) |col| {
                const idx = (row * this.size.x) + col;
                const cs = s[idx];
                const cvs = vs[idx];

                // update the latest found cursor position
                if (cvs.style.cursor) {
                    assert(cursor_position == null);
                    cursor_position = .{
                        .x = @truncate(col),
                        .y = @truncate(row),
                    };
                }

                if (cs.eql(cvs)) continue;

                // render differences found in virtual screen
                try terminal.setCursorPosition(.{ .y = @truncate(row), .x = @truncate(col) });
                try cvs.value(&writer);
                // update screen to be the virtual screen for the next frame
                s[idx] = vs[idx];
            }
        }
        if (cursor_position) |point| {
            try terminal.showCursor();
            try terminal.setCursorPosition(point);
        }
    }
};

const std = @import("std");
const meta = std.meta;
const assert = std.debug.assert;
const Allocator = std.mem.Allocator;
const terminal = @import("terminal.zig");
const Cell = @import("cell.zig");
const Point = @import("point.zig").Point;